Some years ago I attended a masterclass given by a well-known English cathedral
organist
who counselled us to be very attentive to our posture at the console. The ideal
(where circumstances allow)
is to have the seat at a height where the heels can comfortably reach the pedals
and to sit far enough forward
on the seat to be at the point of balance. The position of the seat may need to
be adjusted to permit this.
The back should be kept as straight as possible, even when reaching forward to
the most distant manual.
It still sounds like good advice to me.